   #copyright

Upsilon Andromedae d

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   CAPTION: Upsilon Andromedae d

     Extrasolar planet    Lists of extrasolar planets
                      Parent star
   Star                   Upsilon Andromedae A
   Constellation          Andromeda
   Right ascension    (α) 01^h 36^m 47.8^s
   Declination        (δ) +41° 24′ 20″
   Spectral type          F8V
                   Orbital elements
   Semimajor axis     (a) 2.54 ± 0.15 AU
   Eccentricity       (e) 0.258 ± 0.032
   Orbital period     (P) 1290.1 ± 8.4 d
   Inclination        (i)  ?°
   Longitude of
   periastron         (ω) 279 ± 10°
   Time of periastron (τ) 2,448,827 ± 30 JD
               Physical characteristics
   Mass               (m) >3.93 ± 0.33 M[J]
   Radius             (r)  ? R[J]
   Density            (ρ)  ? kg/ m^3
   Temperature        (T)  ? K
                 Discovery information
   Discovery date         1999
   Discoverer(s)          Butler, Marcy et al.
   Detection method       Radial velocity
   Discovery status       Confirmed
                  Other designations
   50 Andromedae d

   Upsilon Andromedae d an extrasolar planet orbiting the Sun-like star
   Upsilon Andromedae A. Its discovery in 1999 by Geoffrey Marcy and R.
   Paul Butler made Upsilon Andromedae the first known star (other than
   the pulsar PSR 1257+12) to host a multiple-planet planetary system.
   Upsilon Andromedae d is the third planet from its star in order of
   distance and the outermost known planet in its planetary system.

Discovery

   Like the majority of known extrasolar planets, Upsilon Andromedae d was
   detected by measuring variations in its star's radial velocity as a
   result of the planet's gravity. This was done by making precise
   measurements of the Doppler shift of the spectrum of Upsilon Andromedae
   A. At the time of discovery, Upsilon Andromedae A was already known to
   host one extrasolar planet, the hot Jupiter Upsilon Andromedae b,
   however by 1999 it was clear that the inner planet could not explain
   the velocity curve.

   In 1999, astronomers at both San Francisco State University and the
   Harvard-Smithsonian Centre for Astrophysics independently concluded
   that a three-planet model best fit the data. The two new planets were
   designated Upsilon Andromedae c and Upsilon Andromedae d.

Orbit and mass

   Like the majority of long- period extrasolar planets, Upsilon
   Andromedae d revolves around its star in an eccentric orbit, more
   eccentric than that of any of the major planets in our solar system
   (including Pluto). The orbit's semimajor axis puts the planet in the
   habitable zone of Upsilon Andromedae A.

   The planet's orbital eccentricity may be the result of a close
   encounter with a (now lost) outer planet of Upsilon Andromedae A. The
   encounter would have moved Upsilon Andromedae d into an eccentric orbit
   closer to the star and ejected the outer planet from the system.
   Subsequently gravitational perturbations from Upsilon Andromedae d
   moved the inner planet Upsilon Andromedae c into its present eccentric
   orbit.

   A limitation of the radial velocity technique used to discover Upsilon
   Andromedae d is that only a lower limit on the planet's mass can be
   obtained. In the case of Upsilon Andromedae d, this lower limit is 3.93
   times the mass of Jupiter, though depending on the inclination of the
   orbit, the true mass may be much greater than this value. Preliminary
   astrometric measurements suggest the orbit of Upsilon Andromedae d may
   be inclined at 155.5° to the plane of the sky. If these measurements
   are confirmed, this implies that the true mass may be around 9-10 times
   that of Jupiter.

Characteristics

   Given the planet's high mass, it is likely that it is a gas giant with
   no solid surface. Since the planet has only been detected indirectly
   through observations of its star, properties such as its radius,
   composition and temperature are unknown. Assuming a composition similar
   to Jupiter and an environment close to chemical equilibrium, it is
   predicted that its upper atmosphere will contain clouds of water,
   rather than the ammonia clouds typical of Jupiter.

   Upsilon Andromedae d lies in the habitable zone of Upsilon Andromedae A
   as defined both by the ability for an Earthlike world to retain liquid
   water at its surface and based on the amount of ultraviolet radiation
   received from the star. Simulations suggest that even on eccentric
   orbits, terrestrial planets may be able to support liquid water
   throughout the year. This suggests that large moons of Upsilon
   Andromedae d may be able to support extraterrestrial life. On the other
   hand, models of satellite formation around gas giant planets suggest
   that the formation of moons much larger than Mars may be unlikely, as
   there seems to be a common mass ratio between the gas giant and its
   satellite system. In any case, the detection of satellites orbiting
   extrasolar planets is currently beyond our observational capabilities.
   Retrieved from " http://en.wikipedia.org/wiki/Upsilon_Andromedae_d"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
